Graphene sheet and process of preparing the same

ABSTRACT

Provided are a graphene sheet and a process of preparing the same. Particularly, a process of economically preparing a large-area graphene sheet having a desired thickness and a graphene sheet prepared by the process are provided.

This application claims priority to Korean Patent Application No.10-2007-0091642, filed on Sep. 10, 2007, in the Korean IntellectualProperty Office, and all the benefits accruing therefrom under 35 U.S.C.§ 119, the contents of which are incorporated herein in their entiretyby reference.

BACKGROUND OF THE INVENTION

This disclosure relates to a graphene sheet and a process of preparingthe same. In particular, this disclosure also relates to a process ofeconomically manufacturing a graphene sheet having a large area andhaving a desired thickness.

Generally, graphite is a multi-layered stack of two-dimensional graphenesheets formed from a planar array of carbon atoms bonded into hexagonalstructures. Single-layered or multi-layered graphene sheets havebeneficial properties in the area of electrical conductivity.

One noticeable beneficial property is that electrons flow in an entirelyunhindered fashion in a graphene sheet, which is to say that theelectrons flow at the velocity of light in a vacuum. In addition, anunusual half-integer quantum Hall effect for both electrons and holes isobserved in these graphene sheet.

The electron mobility in graphene sheets is about 20,000 to about 50,000square centimeter per volt second (cm²/Vs). In addition, it isadvantageous to use graphene sheets since products made from graphiteare inexpensive while similar products made using carbon nanotubes areexpensive due to low yields during the synthesis and the purificationprocesses. This high cost occurs despite the fact that the carbonnanotubes themselves are inexpensive. Single wall carbon nanotubesexhibit different metallic and semiconducting properties that aredependent upon their chirality and diameter. Furthermore, single wallcarbon nanotubes having similar semiconducting characteristics havedifferent energy band gaps depending upon their chirality and diameter.Thus, in order to obtain a metallic single wall carbon nanotubecomposition or a semiconducting single wall carbon nanotube composition,it is desirable to separate the single wall carbon nanotubes from eachother in order to obtain desired metallic or semiconductingcharacteristics respectively. However, separating the single wall carbonnanotubes is not a simple or inexpensive process.

On the other hand, it may be advantageous to use graphene sheets insteadof carbon nanotubes since it may be possible to design a device thatexhibits desired electrical characteristics by arranging the crystallineorientation in a suitable desired direction since electricalcharacteristics of a graphene sheet are changed according to thecrystalline orientation. These characteristics of the graphene sheet maybe advantageously used in carbonaceous electrical devices orcarbonaceous electromagnetic devices of the future.

However, although the graphene sheet has these advantageouscharacteristics, a method of economically and reproducibly preparing alarge-area graphene sheet has not yet been developed. Methods ofpreparing graphene sheets are classified into micromechanical methodsand a silicon carbide (SiC) thermal decomposition method.

In the micromechanical method, a tape having a layer of adhesive on itsuch as, or example, a SCOTCH™ tape is applied against a graphitesurface that has graphene layers preferably stacked in parallel. Thegraphene layers attach to the SCOTCH™ tape, which is subsequentlyremoved from the graphite surface. The graphene layers are then removedfrom the SCOTCH™ tape. The graphene layers that are removed by theSCOTCH™ tape are however, not uniform in size nor do they have uniformshapes. In addition, graphene sheets having large surface areas cannotbe extracted by this method. This makes their use questionable or evenundesirable in certain applications.

In the SiC thermal decomposition method, a single crystal SiC is heatedto remove Si by decomposing the SiC on the surface, and then residualcarbon C forms on a graphene sheet. However, the single crystal SiC usedin SiC thermal decomposition is very expensive, and a large-areagraphene sheet cannot be easily manufactured.

SUMMARY OF THE INVENTION

Disclosed herein a process of economically preparing a large-areagraphene sheet having a desired thickness.

Disclosed herein too is a graphene sheet prepared by the process.

Disclosed herein too are articles manufactured from the graphene sheetderived from the aforementioned process. The articles include amembrane, a hydrogen storage medium, an optical fiber and an electricaldevice.

Disclosed herein too is a graphene substrate that comprises theaforementioned graphene sheet.

Disclosed herein too is a process for preparing a graphene sheet, theprocess including forming a graphitizing catalyst in the form of asheet; coating a polymer on the graphitizing catalyst; and heat-treatingthe graphitizing catalyst in an inert or reductive atmosphere to form agraphene sheet.

The graphitizing catalyst may be a catalytic metal. The catalytic metalcan be a transition metal. In one embodiment, the catalytic metal isselected from the group consisting of Ni, Co, Fe, Pt, Au, Al, Cr, Cu,Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V and Zr.

The polymer may be a self-assembling polymer.

The polymer may be selected from the group consisting of an amphiphilicpolymer, a liquid crystal polymer and a conductive polymer.

The amphiphilic polymer may include a hydrophilic group; the hydrophilicgroup being selected from the group consisting of an amino group, ahydroxyl group, a carboxyl group, a sulfate group, a sulfonate group, aphosphate group, a phosphonate group, and salts thereof; and ahydrophobic group; the hydrophobic group being selected from the groupconsisting of a halogen atom, a C1-C30 alkyl group, a C1-C30 halogenatedalkyl group, a C2-C30 alkenyl group, a C2-C30 halogenated alkenyl group,a C2-C30 alkynyl group, a C2-C30 halogenated alkynyl group, a C1-C30alkoxy group, a C1-C30 halogenated alkoxy group, a C1-C30 hetero alkylgroup, a C1-C30 halogenated hetero alkyl group, a C6-C30 aryl group, aC6-C30 halogenated aryl group, a C7-C30 arylalkyl group and a C7-C30halogenated arylalkyl group.

The amphiphilic polymer is selected from the group consisting of capricacid, lauric acid, palmitic acid, stearic acid, myristoleic acid,palmitolic acid, oleic acid, stearidonic acid, linolenic acid, caprylamine, lauryl amine, stearyl amine and oleyl amine.

The conductive polymer is selected from the group consisting ofpolyacetylene, polypyrrole, polythiophene, polyaniline, polyfluorene,poly(3-hexylthiophene), polynaphthalene, poly(p-phenylene sulfide) andpoly(p-phenylene vinylene).

The conductive polymer is selected from the group consisting of aceneand its derivatives, hetero acene and its derivatives, anthracene andits derivatives, hetero anthracene and its derivatives, tetracene andits derivatives, hetero tetracene and its derivatives, pentacene and itsderivatives, and hetero pentacene and its derivatives.

The polymer may include a polymerizable functional group, i.e., apolymeric precursor having a polymerizable functional group may bedisposed upon the graphitizing catalyst and then subjected topolymerization upon being disposed on the graphitizing catalyst.Polymeric precursors may include monomers, dimers, trimers, pentamers,or the like. Even larger polymeric species having about 10 to about 100repeat units and having suitable functional groups can be disposed uponthe graphitizing catalyst and then subjected to polymerization.

After disposing a polymer on the graphitizing catalyst, a heat treatmentmay be performed at a temperature of about 400 to about 2,000° C. forabout 0.1 to about 10 hours.

The graphitizing catalyst may be immobilized on a substrate.

The process may further include separating the graphite sheet byremoving the graphitizing catalyst using an acid-treatment. This acidtreatment is done after the heat-treatment.

The thickness of the graphene sheet may be controlled by adjusting theamount of the polymer.

The heat-treatment may be performed by induction heating, radiating heatenergy, laser, infrared rays (IR), microwaves, plasma, ultraviolet (UV)rays or surface plasmon heating.

The heat-treatment may be selectively applied to the graphitizingcatalyst.

The graphene sheet may be formed of polycyclic aromatic molecules inwhich a plurality of carbon atoms are covalently bound to each other.The graphene sheet may have 1 to 300 layers and the width and length ofeach graphene sheet may be about 1 mm or longer.

The graphene sheet may have about 1 to about 60 layers, and preferablyabout 1 to about 15 layers.

The width and length of the graphene sheet may be each from about 1 toabout 1,000 mm.

The width and length of the graphene sheet may respectively be longerthan about 10 mm.

Disclosed herein too is an article comprising a graphene substratehaving a graphene sheet disposed thereon.

The graphene substrate may further include a graphitizing catalyst layerinterposed between the substrate and the graphene sheet.

The substrate may be silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is an exemplary depiction that schematically shows a process ofpreparing a graphene sheet;

FIG. 2 is an exemplary depiction that schematically shows a polymercoated on a catalyst;

FIG. 3 is an exemplary depiction that schematically shows a structure ofa graphene sheet formed on a catalyst; and

FIG. 4 is an exemplary depiction that schematically shows a stack ofpolymers having a hydrophilic part and a hydrophobic part.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will now be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “disposed on” or “formed on” another element, theelements are understood to be in at least partial contact with eachother, unless otherwise specified.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The use of the terms “first”, “second”, and the like do notimply any particular order but are included to identify individualelements. It will be further understood that the terms “comprises”and/or “comprising”, or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Disclosed herein is a process of economically preparing graphene sheetshaving a large surface area that are of a desired thickness. Thegraphene sheet can be advantageously used in numerous articles.

The term “graphene sheet” as used herein indicates graphene in the formof a sheet formed of polycyclic aromatic molecules in which a pluralityof carbon atoms are covalently bound to each other. The covalently boundcarbon atoms form 6-membered rings (which is the predominant repeatingunit of the graphene sheet), but can also form 5-membered rings and/or7-membered rings. Accordingly, in the graphene sheet it appears as ifthe covalently bound carbon atoms (usually, sp² bond) form a singlelayer. The graphene sheet may have various structures and the structuremay vary according to the amount of the 5-membered rings and/or the7-membered rings present in the graphene sheet. The graphene sheet mayhave not only a single layer of graphene, but may also be multi-layeredcomprising a plurality of layers up to 300 layers. Generally, the endsof the graphene are saturated with hydrogen atoms.

The graphene sheet may be formed by coating a polymer on a graphitizingcatalyst to form a coated graphitizing catalyst, and heat-treating theresultant coated graphitizing catalyst in an inert or reductiveatmosphere as shown in FIG. 1. During the heat-treatment, the polymerundergoes degradation and other components of the polymer except for thecarbon atoms are evaporated. The residual carbon atoms that remain uponthe graphitizing catalyst are bound to each other in a planar hexagonalstructure to form the graphene sheet.

The graphitizing catalyst binds carbon atoms included in the polymer andassists the formation of the planar hexagonal structure of the carbonatoms. For example, any catalyst used to synthesize graphite, inducecarbonization or manufacture carbon nanotubes can be used as thegraphitizing catalyst. The catalyst may comprise a catalytic metal.Examples of catalytic metals are transition metal catalysts. Other metalcatalysts can be used as well. Transition metal catalysts can be alloyedwith other metal catalysts. The catalyst may be at least one selectedfrom the group consisting of nickel (Ni), cobalt (Co), iron (Fe),platinum (Pt), gold (Au), aluminum (Al), chromium (Cr), copper (Cu),magnesium (Mg), manganese (Mn), molybdenum (Mo), rhodium (Rh), silicon(Si), tantalum (Ta), titanium (Ti), tungsten (W), uranium (U), vanadium(V) and zirconium (Zr). In one embodiment, the graphitizing catalyst maybe in the form of a plate or sheet that comprises the catalytic metal.In another embodiment, the graphitizing catalyst can comprise acatalytic metal that is immobilized on a substrate by deposition,sputtering, or the like.

Any polymer that includes carbon atoms can be coated on the graphitizingcatalyst, and the structure and composition of the polymer are notlimited. It is therefore desirable to use an organic polymer to coat thegraphitizing catalyst. A polymer that forms a dense coating can be usedin order to form a dense graphite layer.

The organic polymer that is disposed on the graphitizing catalyst may beselected from a wide variety of thermoplastic polymers, thermosettingpolymers, blends of thermoplastic polymers, blends of thermosettingpolymers, or blends of thermoplastic polymers with thermosettingpolymers. The thermoplastic polymer may also be a blend of polymers,copolymers, terpolymers, or combinations comprising at least one of theforegoing thermoplastic polymers. The thermoplastic polymer can also bean oligomer, a homopolymer, a copolymer, a block copolymer, analternating block copolymer, a random polymer, a random copolymer, arandom block copolymer, a graft copolymer, a star block copolymer, adendrimer, or the like, or a combination comprising at last one of theforegoing thermoplastic polymers.

In general, when polymers disposed on the graphitizing catalyst throughspin coating, dip coating, or the like, they form an irregular networkstructure and are irregularly arranged, and thus the graphite layercannot have a dense structure. On the other hand, when a self-assemblingpolymer is disposed upon on the graphitizing catalyst, the polymer isregularly arranged in vertical directions on the surface of thegraphitizing catalyst as shown in FIG. 2, and thus a graphene sheethaving a dense structure can be prepared as shown in FIG. 3.

Any self-assembling polymer can be disposed upon the graphitizingcatalyst without limitation. For example, the self-assembling polymercan be selected from the group consisting of an amphiphilic polymer, aliquid crystal polymer and a conductive polymer.

The amphiphilic polymer includes both a hydrophilic group and ahydrophobic group, and thus can be arranged in a uniform direction in awater soluble solution. For example, Langmuir-Blodgett arrangements,dipping arrangements and spin arrangements are possible,

The amphiphilic polymer includes a hydrophilic group having at least oneof an amino group, a hydroxyl group, a carboxyl group, a sulfate group,a sulfonate group, a phosphate group, a phosphonate group, and saltsthereof; and a hydrophobic group having at least one of a halogen atom,a C1-C30 alkyl group, a C1-C30 halogenated alkyl group, a C2-C30 alkenylgroup, a C2-C30 halogenated alkenyl group, a C2-C30 alkynyl group, aC2-C30 halogenated alkynyl group, a C1-C30 alkoxy group, a C1-C30halogenated alkoxy group, a C1-C30 hetero alkyl group, a C1-C30halogenated hetero alkyl group, a C6-C30 aryl group, a C6-C30halogenated aryl group, a C7-C30 arylalkyl group and a C7-C30halogenated arylalkyl group. Examples of the amphiphilic polymer arecapric acid, lauric acid, palmitic acid, stearic acid, myristoleic acid,palmitolic acid, oleic acid, stearidonic acid, linolenic acid, caprylamine, lauryl amine, stearyl amine and oleyl amine.

The liquid crystal polymer can be arranged in a uniform direction in aliquid state so as to form an oriented liquid crystal polymer. Theconductive polymer is dissolved in a solvent to form a membrane and canform a crystalline structure by being aligned after the solvent isevaporated. Thus, the polymers can be aligned on the graphitizingcatalyst by processes that facilitate orientation such as for example,spin coating, or the like. Examples of the conductive polymer arepolyacetylene, polypyrrole, polythiophene, polyaniline, polyfluorene,poly(3-hexylthiophene), polynaphthalene, poly(p-phenylene sulfide) andpoly(p-phenylene vinylene).

Copolymers or blends of conductive polymers with other non-electricallyconducting organic polymers may also be disposed on the graphitizingcatalyst. Examples of non-electrically conducting organic polymers thatcan be copolymerized or blended with the electrically conductive polymerare polymethylmethacrylates, polyacrylates, polyamides, polyesters,polyetherketones, polyether ether ketones, polyether ketone ketones,polycarbonates, polyarylene ethers, epoxies, polysulfones,polyethersulfones, polyetherimides, or the like, or combinationscomprising at least one of the foregoing polymers.

Meanwhile, polymers that are automatically aligned when deposited fromvapor state can be used. Electrically conducting polymers that can bedisposed upon the graphitizing catalyst from the vapor state and whichundergo alignment upon being disposed can also be used. Examples of suchconductive polymers are acene and its derivatives, anthracene and itsderivatives, hetero anthracene (e.g., benzodithiophene anddithienothiophene) and its derivatives, tetracene and its derivatives(e.g., halogenated tetracene, tetracene derivatives having a polarsubstituent, tetracene-thiophene hybrid materials, rubrene and alkyl-and alkoxy-substituted tetracene), hetero tetracene and its derivatives,pentacene and its derivatives (e.g., alkyl- and halogen-substitutedpentacene, aryl-substituted pentacene, alkynyl-substituted pentacene,alkynyl-substituted alkyl and alkynyl pentacene and alkynyl-substitutedpentacene ether), hetero pentacene and its derivatives, and hetero aceneand its derivatives.

The polymer may include at least one polymerizable functional groupcapable of forming a carbon-carbon double bond or triple bond. Thepolymerizable functional group can induce polymerization of polymersthrough a process of polymerization such as UV irradiation after thepolymer layer is formed. Since the polymer thus formed has a largemolecular weight, evaporation of carbon can be prevented during theheat-treatment of the polymer.

The polymerization of the polymer may be performed before or aftercoating the polymer on the graphitizing catalyst. That is, when thepolymerization is conducted prior to coating the polymer on thegraphitizing catalyst, the polymer layer on the graphitization layer canbe formed by transferring a polymer membrane onto the graphitizingcatalyst. The polymerization and transfer can be repeated several timesto control the thickness of the graphene sheet.

The polymer can be aligned on the surface of the graphitizing catalystusing various coating methods, such as Langmuir-Blodgett, dip coating,spin coating and vacuum deposition. The molecular weight of the alignedpolymer, thickness of the polymer layer or the number of self-assemblingpolymer layers may vary depending on a desired number of layers of thegraphene sheet. That is, use of a polymer having a large molecularweight increases the number of layers of the graphene sheet since thepolymer has a large amount of carbon. As the thickness of the polymerlayer increases, the number of layers of the generated graphene sheet isincreased, and thus the thickness of the graphene sheet is alsoincreased. The thickness of the graphene sheet can be controlled usingthe molecular weight of the polymer.

In addition, the amphiphilic polymer, which is a self-assembling polymerincludes a hydrophilic part and a hydrophobic part in a single polymericmolecule. As shown in FIG. 4, the hydrophilic part of the polymercombines with the hydrophilic graphitizing catalyst so as to beuniformly aligned on the catalyst layer, and the hydrophobic part of theamphiphilic polymer is aligned in the opposite direction to be combinedwith the hydrophilic part of another amphiphilic polymer that is notcombined with the catalyst layer. When the amount of the amphiphilicpolymer is sufficient, the amphiphilic polymer can be stacked on thecatalyst layer by the hydrophilic-hydrophobic bonds. The stacked layersformed of a plurality of the amphiphilic polymers can form a graphenelayer by heat-treatment. Thus, a graphene sheet having a desiredthickness can be prepared since the number of layers of the graphenesheet can be controlled by selecting an appropriate amphiphilic polymerand adjusting the amount of the amphiphilic polymer.

The number of layers of the graphene sheets may be from about 1 up toabout 30°, preferably in the range of about 1 to about 60, and morepreferably in the range of about 1 to about 15. A graphene sheet havingover about 300 layers is regarded as graphite, which is not within thescope of the present invention.

The area of the graphene sheet is dependent upon the size of thesubstrate and is controlled by regulating the size of the substrate onwhich the graphitizing catalyst is formed, and thus a large-areagraphene sheet can be prepared without difficulty. That is, a large-areagraphene sheet can be prepared by preparing a substrate having a largesurface area, for example, a substrate having an area greater than 1millimeter (mm)×1 mm, and preferably in the range of about 1 mm×1 mm (1mm²) to about 1,000 mm×1,000 (10⁶ mm²) mm, forming a graphitizingcatalyst on the substrate using various methods, coating the polymer onthe graphitizing catalyst, and heat-treating the resultant. Accordingly,the area of the graphene sheet can be adjusted by merely controlling thesize of the substrate. The substrate may be a silicon substrate, but isnot limited thereto.

As described above, the width and length of the graphene sheet may berespectively about 1 mm or longer, preferably about 10 mm or longer, andmore preferably in the range of about 10 mm to about 1,000 mm. When thelength of the graphene sheet is greater than about 1,000 mm, propertiesof the graphene sheet can be degraded since the deficiencies in thegraphene sheet may be substantially increased.

The polymer coated on the graphitizing catalyst is heat-treated tographitize the polymer. The heat-treatment can be performed in an inertor reductive atmosphere in order to prevent oxidation of the elements ofthe polymer. The heat-treatment is performed at a temperature of about400 to about 2,000° C. When the temperature is lower than about 400° C.,the graphitization cannot be sufficiently performed. On the other hand,when the temperature is higher than about 2,000° C., carbon may beevaporated. The heat-treatment may be performed for about 0.1 to about10 hours. When the heat-treatment time is not within the range describedabove, the graphitization cannot be sufficiently performed or costs maybe increased.

The heat-treatment may be performed by using sources of electromagneticradiation. In one embodiment, the heat treatment can be accomplishedusing induction heatings, radiated energy, laser, infrared rays (IR),microwaves, plasma, ultraviolet (UV) rays or surface plasmon heatingswithout limitation. In another embodiment, it is desirable for thegraphitizing catalyst on which the polymer is coated to be activated byselectively heating the catalyst by induction heating or by usingmicrowaves. Thus, a specific region can be graphitized, and asingle-layered graphene sheet can be prepared by graphitizing a polymerof a small thickness. The carbon atoms can be covalently bound to eachother by the heat-treatment. For example, the carbon atoms form a planarhexagonal structure to form the graphene sheet on the substrate, andthus the graphene sheet forms a graphene substrate with the substrate.Herein, the term “graphene substrate” indicates a combination of thesubstrate and the graphene sheet formed on the substrate.

Thus formed graphene sheet exists on the substrate and the graphitizingcatalyst layer. The graphene sheet can be used with the graphitizingcatalyst, or alternatively, the graphene sheet can be used, if required,by dissolving and removing the graphitizing catalyst by anacid-treatment. If required, the graphene sheet may be separated fromthe substrate.

An exemplary acid used for separating the graphene sheet from thegraphitizing catalyst is an HCl solution.

The separated graphene sheet can be processed in a variety of waysaccording to its desired use. That is, the graphene sheet can be cutinto a predetermined shape, or can be wound to form a tube. Theprocessed graphene sheet can be combined with a desired subject forapplications.

The graphene sheet can be applied in various fields. The graphene sheetcan be efficiently used in a transparent electrode since it hasexcellent conductivity and high uniformity. An electrode that is used ona substrate of solar cells, or the like, can be formed to meettransparency requirements since light needs to penetrate therethrough.The graphene sheet when used in a transparent electrode has excellentconductivity. In addition, the flexibility of the graphene sheet permitsit to be used in a flexible transparent electrode. A flexible solar cellcan be prepared by using a flexible plastic as a substrate with thegraphene sheet as a transparent electrode being disposed upon theflexible plastic. In addition, when the graphene sheet is used as aconductive thin film for various display devices, the desiredconductivity can be achieved using only a small amount of electricalenergy. In addition, the light penetration can be improved.

In addition, the graphene sheet formed in the form of a tube can be usedas an optical fiber, a hydrogen storage medium or a membrane thatselectively allows hydrogen to penetrate.

The present invention provides a process for economically preparing alarge-area graphene sheet, and efficiently controlling the thickness ofthe graphene sheet. The graphene sheet can be efficiently applied to atransparent electrode, a hydrogen storage medium, an optical fiber, anelectrical device, or the like since a large-area graphene sheet havinga desired thickness can be obtained.

The present invention will now be described in greater detail withreference to the following examples. The following examples are forillustrative purposes only and are not intended to limit the scope ofthe invention.

EXAMPLES Example 1

Ni was deposited on a 3 centimeter (cm)×3 cm silicon substrate on which100 nanometers (nm) of SiO₂ was coated using sputtering to form a Nithin film. An oleic acid solution having a concentration of 1 milligramper milliliter (mg/ml) (in chloroform) was prepared by dissolving oleicacid in chloroform. 50 microliters (μl) of the oleic acid solution wasadded to a Langmuir-Blodgett (LB) device that contained water. After theoleic acid solution was added, a self assembled monolayer (SAM) wasprepared using the LB device. 254 nm ultraviolet (UV) radiation was usedto polymerize the SAM layer formed of oleic acid. The obtained oleicacid SAM was transferred to a 3 cm×3 cm silicon substrate on which 100nm of SiO₂ was coated.

Then, the oleic acid coated substrate was heated in a vacuum at 60° C.for 12 hours and dried. The dried oleic acid coated substrate washeat-treated in a furnace under a nitrogen atmosphere 500° C. for 1 hourto prepare a substrate having an area of 3 cm×3 cm and a single-layeredgraphene sheet. Then, the substrate including the graphene sheet wasimmersed in 0.1 M HCl for 24 hours to remove the Ni thin film. Thegraphene sheet was thus separated.

Example 2

A 3 cm×3 cm graphene sheet having about 10 layers was prepared in thesame manner as in Example 1, except that transferring of the oleic acidSAM polymerized according to Example 1 to the silicon substrate wasrepeated 10 times.

Example 3

A 3 cm×3 cm graphene sheet having about 21 layers was prepared in thesame manner as in Example 1, except that transferring of the oleic acidSAM polymerized according to Example 1 to the silicon substrate wasrepeated 20 times.

Example 4

A 3 cm×3 cm graphene sheet having about 43 layers was prepared in thesame manner as in Example 1, except that transferring of the oleic acidSAM polymerized according to Example 1 to the silicon substrate wasrepeated 40 times.

Example 5

Ni was deposited on a silicon substrate having a diameter of 4 inches onwhich 100 nm of SiO₂ was coated using sputtering to form a Ni thin film.The substrate on which Ni was immobilized was immersed in a mixedsolution of 0.1 L of water and 100 μg of oleic acid and stirred at 200rpm. After 4 hours, the substrate was heated in a vacuum at 60° C. for12 hours to remove water. The dried oleic acid coated substrate washeat-treated under a nitrogen atmosphere in a furnace at 500° C. for 1to obtain a graphene sheet having about 3 layers that were 4 inches indiameter.

Then, the substrate including the graphene sheet was immersed in 0.1 MHCl for 24 hours to remove the Ni thin film and the graphene sheet wasseparated.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention.

1. A process of preparing a graphene sheet, the process comprising:forming a graphitizing catalyst in the form of a sheet; disposing apolymer on the graphitizing catalyst; and heat-treating the polymer onthe graphitizing catalyst in an inert or reductive atmosphere to form agraphene sheet.
 2. The process of claim 1, wherein the graphitizingcatalyst is at least one catalyst selected from the group consisting ofNi, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V andZr.
 3. The process of claim 1, wherein the polymer is a self-assemblingpolymer.
 4. The process of claim 1, wherein the polymer is selected fromthe group consisting of an amphiphilic polymer, a liquid crystal polymerand a conductive polymer.
 5. The process of claim 4, wherein theamphiphilic polymer comprises: a hydrophilic group selected from thegroup consisting of an amino group, a hydroxyl group, a carboxyl group,a sulfate group, a sulfonate group, a phosphate group and salts thereof;and a hydrophobic group having at least one selected from the groupconsisting of a halogen atom, a C1-C30 alkyl group, a C1-C30 halogenatedalkyl group, a C2-C30 alkenyl group, a C2-C30 halogenated alkenyl group,a C2-C30 alkynyl group, a C2-C30 halogenated alkynyl group, a C1-C30alkoxy group, a C1-C30 halogenated alkoxy group, a C1-C30 hetero alkylgroup, a C1-C30 halogenated hetero alkyl group, a C6-C30 aryl group, aC6-C30 halogenated aryl group, a C7-C30 arylalkyl group and a C7-C30halogenated arylalkyl group.
 6. The process of claim 4, wherein theamphiphilic polymer is selected from the group consisting of capricacid, lauric acid, palmitic acid, stearic acid, myristoleic acid,palmitolic acid, oleic acid, stearidonic acid, linolenic acid, caprylamine, lauryl amine, stearyl amine and oleyl amine.
 7. The process ofclaim 4, wherein the conductive polymer selected from the groupconsisting of polyacetylene, polypyrrole, polythiophene, polyaniline,polyfluorene, poly(3-hexylthiophene), polynaphthalene, poly(p-phenylenesulfide) and poly(p-phenylene vinylene).
 8. The process of claim 4,wherein the conductive polymer is selected from the group consisting ofacene and its derivatives, hetero acene and its derivatives, anthraceneand its derivatives, hetero anthracene and its derivatives, tetraceneand its derivatives, hetero tetracene and its derivatives, pentacene andits derivatives, and hetero pentacene and its derivatives.
 9. Theprocess of claim 1, wherein the polymer comprises a polymerizablefunctional group.
 10. The process of claim 9, further comprisingpolymerizing the polymer prior to disposing the polymer on thegraphitizing catalyst.
 11. The process of claim 9, further comprisingpolymerizing the polymer including the polymerizable functional groupafter coating the polymer or a polymer precursor on the graphitizingcatalyst.
 12. The process of claim 1, wherein the heat-treating isperformed at a temperature of about 400 to about 2,000° C. for about 0.1to about 10 hours.
 13. The process of claim 1, wherein the graphitizingcatalyst is immobilized on a substrate.
 14. The process of claim 1,further comprising separating the graphene sheet from the graphitizingcatalyst by using an acid-treatment after the heat-treatment.
 15. Theprocess of claim 1, wherein the thickness of the graphene sheet iscontrolled by adjusting the amount of the polymer that is disposed uponthe graphitizing catalyst.
 16. The process of claim 1, wherein theheat-treatment is performed by induction heating, radiating heat energy,laser, infrared rays, microwaves, plasma, ultraviolet rays or surfaceplasmon heating.
 17. The process of claim 1, wherein the heat-treatmentis selectively applied to the graphitizing catalyst.
 18. The process ofclaim 1, wherein the polymer is a thermoplastic polymer, a thermosettingpolymer, a blend of thermoplastic polymers, a blend of thermosettingpolymers, or a blend of a thermoplastic polymer with a thermosettingpolymer.
 19. The process of claim 1, wherein the polymer is a anoligomer, a homopolymer, a copolymer, a block copolymer, an alternatingblock copolymer, a random copolymer, a random block copolymer, a graftcopolymer, a star block copolymer, a dendrimer, or a combinationcomprising at last one of the foregoing polymers.
 20. The process ofclaim 4, wherein the conducting polymer is further copolymerized with anelectrically non-conducting polymer.
 21. A graphene sheet prepared bythe process of claim
 1. 22. A process of preparing a graphene sheet, theprocess comprising: disposing upon a silicon substrate a graphitizingcatalyst; the graphitizing catalyst being in intimate contact with thesilicon substrate; disposing a polymer on the graphitizing catalyst; andheat-treating the polymer on the graphitizing catalyst to form agraphene sheet.
 23. The process of claim 22, wherein the heat treatingis conducted in an inert or reductive atmosphere.
 24. The process ofclaim 22, further comprising separating the graphene sheet from thegraphitizing catalyst in an acid solution.
 25. A graphene sheetcomprising: polycyclic aromatic molecules in which a plurality of carbonatoms are covalently bound to each other, wherein the graphene sheet hasabout 1 to about 300 layers and wherein the width and length of thegraphene sheet are each about 1 mm or longer.
 26. The graphene sheet ofclaim 25, wherein the graphene sheet has about 1 to about 60 layers. 27.The graphene sheet of claim 25, wherein the graphene sheet has about 1to about 15 layers.
 28. The graphene sheet of claim 25, wherein thewidth and length of the graphene sheet are each from about 1 to about1,000 mm.
 29. A hydrogen storage medium comprising a graphene sheetaccording to claim
 25. 30. An electrical device comprising a graphenesheet according to claim
 25. 31. A graphene substrate comprising: asubstrate; and a graphene sheet according to claim 25 being formed onthe substrate.
 32. The graphene substrate of claim 31, furthercomprising a graphitizing catalyst layer interposed between thesubstrate and the graphene sheet.
 33. The graphene substrate of claim31, wherein the substrate is silicon.